Transcript Bits Are Distorted By.........

Attenuation is the loss of signal strength, for example, when cables
exceed a maximum length. This means that a 1 bit voltage signal loses
amplitude as energy passes from the signal to the cable. While
choosing materials carefully, (e.g. using copper instead of carbon),
and geometry (the shape and positioning of the wires) can reduce
electrical attenuation. Some loss is always unavoidable when electrical
resistance is present. Attenuation also happens to optical signals; the
optical fiber absorbs and scatters some of the light energy as the light
pulse, 1 bit, travels down the fiber. This can be minimized by the
wavelength, or color, of the light that you choose. This can also be
minimized by whether or not you use single mode or multi-mode
fiber, and by the actual glass that is used for the fiber. Even with these
choices, some signal loss is unavoidable.
Reflection occurs in electrical signals. When voltage pulses, or bits, hit a discontinuity some
energy can be reflected. If not carefully controlled, this energy can interfere with later bits.
Remember, while you are focused on only 1 bit at a time right now, in real networks you will
want to send millions and billions of bits every second, thus requiring you to keep track of this
reflected pulse energy. Depending on the cabling and connections that the network uses,
reflections may or may not be a problem.
Dispersion is when the signal broadens in time. It is caused by the type of
media involved. If serious enough, 1 bit can start to interfere with the next
bit and confuse it with the bits before and after it. Since you want to send
billions of bits per second, you must be careful not to allow the signals to
spread out . Dispersion can be fixed by proper cable design, limiting
cable lengths, and finding the proper impedance. In optical fibers,
dispersion can be controlled by using laser light of a very specific
wavelength. For wireless communications, dispersion can be minimized
by the frequencies used to transmit. Latency, also known as delay, has
two main causes. First, Einstein’s theory of relativity states, "nothing can
travel faster than the speed of light in a vacuum (3.0 x 108
meters/second)." Wireless networking signals travel at slightly less than
the speed of light in vacuum. Networking signals on copper media they
travel in the range of 1.9x108 m/s to 2.4x108 m/s. Networking signals on
optical fiber travel at approximately 2.0x108 m/s. So to travel a distance, a
bit takes at least a small amount of time to get to where it’s going.
Second, if the bit goes through any devices, the transistors and
electronics introduce more latency. The solution to the problem of latency
Propagation means travel. When a NIC puts out a voltage or light pulse onto
a physical medium, that square pulse made up of waves travels along the
medium (propagates). Propagation means that a lump of energy,
representing 1 bit, travels from one place to another. The speed at which it
propagates depends on the actual material used in the medium, the
geometry (structure) of the medium, and the frequency of the pulses.
Noise is unwanted additions to voltage, optical, or
electromagnetic signals. No electrical signal is without noise,
however, it is important to keep the signal-to-noise (S/N) ratio
as high as possible. The S/N ratio is an engineering
calculation and measurement which involves dividing the
signal strength by the noise strength; it gives a measure of
how easy it will be to decipher the desired, intended signal
from the unwanted, but unavoidable, noise. In other words,
each bit receives additional unwanted signals from various
sources. Too much noise can corrupt a bit turning a binary 1
into a binary 0, or a 0 into a 1, destroying the message.
A collision occurs when two bits from two different
communicating computers are on a shared-medium at the
same time. In the case of copper media, the voltages of the
two binary signals are added, and cause a third voltage level.
This voltage variation is not allowed in a binary system,
which only understands two voltage levels. The bits are
corrupted "destroyed".
Some technologies, such as Ethernet, deal with a certain
quantity of collisions to negotiate whose turn it is to transmit
on the shared media when communicating between hosts. In
some instances collisions are a natural part of the
functioning of a network. However, excessive collisions can